Field of the Invention
This application relates to communication cables. More particularly, this application relates to network cable construction.
Description of Related Art
Communication cables are broadly grouped into two arrangements, fiber optic cables and metal conductor cables, each of which has its own unique set of construction parameters that affect the quality of the communication signals carried therethrough.
Regarding metal conductor cables, one typical arrangement is the LAN (Local Area Network) cable that is usually constructed of four pairs of twisted insulated copper conductors encased within a jacket. Other larger cables may employ ore pairs of conductors.
In this typical four pair LAN cable construction, in addition to the outer jacket, each of the eight primary conductors are individually coated with an insulation layer. Among the other components, LAN cables often include a tape or various extruded shapes including cross-fillers to separate the twisted pairs for better NEXT (Near End Cross Talk) performance.
In each case, aside from electrical performance considerations, there are certain flammability performance tests that need to be met. One such crucial test is the NFPA (National Fire Protection Association) 262 flame test (or UL 910), which is a standard method of testing for flame travel and smoke generation for testing wires and cables that may be installed in air-handling spaces such as budding ductwork.
In this context, FEP (Fluorinated Ethylene Polymer) resin, thanks to its outstanding electrical and flame performance, is a typical material choice for the LAN cable application. Aside from its use as the insulation on the primary conductors of the twisted pairs, FEP is also currently the ideal material choice for tapes or various extruded shapes including cross fillers as it has excellent electrical properties and good flame and smoke performance.
Alternative prior art arrangements have used mixtures of LDPE and VLDPE (Low Density and Very Low Density Polyethylene) with significant quantities of flame retardant fillers blended into the polymer composition. Such highly filled LDPE and/or VLDPE olefin blends are used for cross fillers to reduce cost of the LAN cable. However, even when highly filled with flame retardant fillers, such LDPE and VLDPE polymers still exhibit inferior smoke and flame resistance properties relative to the FEP.
Other polymers exist such as PVC (Poly-Vinyl Chloride) with fire retardant fillers (e.g. FRPVC), however, prior art constructions do not use PVC for CAT 6 LAN tapes or cross fillers to separate twisted pairs because PVC without plasticizing additives tend to be too rigid for cable applications. When plasticizing additives are incorporated into the PVC, they tend to degrade the electrical properties of the PVC causing too much signal attenuation to be useful in most CAT 6 LAN cable applications. For example, the commonly used plasticizers in PVC insulation for wire and cable arrangements are ester based plasticizers which can have a negative effect on the dissipation factor of the final PVC compound.
Generally, there is a dissipation of electrical energy, caused by the presence of dielectric material in close proximity to the wire. The dissipation factor of a dielectric material is a measure of the power loss rate caused by said material. Certain polymers have better (lower) dissipation factors than others. Likewise, the same polymer may exhibit a different dissipation factor depending on different formulations of that polymer (e.g. different additives, flame retardants, processing agents etc incorporated into the polymer).
As shown in prior art FIG. 1, over various frequency ranges, ester based plasticizers (used at 50 phr in PVC) still result in the PVC exhibiting dissipation loss factors in excess of 0.01 at frequencies between 100 MHz to 500 MHz.